man2/prctl.2

   1 .\" Copyright (C) 1998 Andries Brouwer (aeb@cwi.nl)
   2 .\" and Copyright (C) 2002, 2006, 2008, 2012, 2013 Michael Kerrisk <mtk.manpages@gmail.com>
   3 .\" and Copyright Guillem Jover <guillem@hadrons.org>
   4 .\" and Copyright (C) 2014 Dave Hansen / Intel
   5 .\"
   6 .\" %%%LICENSE_START(VERBATIM)
   7 .\" Permission is granted to make and distribute verbatim copies of this
   8 .\" manual provided the copyright notice and this permission notice are
   9 .\" preserved on all copies.
  10 .\"
  11 .\" Permission is granted to copy and distribute modified versions of this
  12 .\" manual under the conditions for verbatim copying, provided that the
  13 .\" entire resulting derived work is distributed under the terms of a
  14 .\" permission notice identical to this one.
  15 .\"
  16 .\" Since the Linux kernel and libraries are constantly changing, this
  17 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  18 .\" responsibility for errors or omissions, or for damages resulting from
  19 .\" the use of the information contained herein.  The author(s) may not
  20 .\" have taken the same level of care in the production of this manual,
  21 .\" which is licensed free of charge, as they might when working
  22 .\" professionally.
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  24 .\" Formatted or processed versions of this manual, if unaccompanied by
  25 .\" the source, must acknowledge the copyright and authors of this work.
  26 .\" %%%LICENSE_END
  27 .\"
  28 .\" Modified Thu Nov 11 04:19:42 MET 1999, aeb: added PR_GET_PDEATHSIG
  29 .\" Modified 27 Jun 02, Michael Kerrisk
  30 .\"     Added PR_SET_DUMPABLE, PR_GET_DUMPABLE,
  31 .\"     PR_SET_KEEPCAPS, PR_GET_KEEPCAPS
  32 .\" Modified 2006-08-30 Guillem Jover <guillem@hadrons.org>
  33 .\"     Updated Linux versions where the options where introduced.
  34 .\"     Added PR_SET_TIMING, PR_GET_TIMING, PR_SET_NAME, PR_GET_NAME,
  35 .\"     PR_SET_UNALIGN, PR_GET_UNALIGN, PR_SET_FPEMU, PR_GET_FPEMU,
  36 .\"     PR_SET_FPEXC, PR_GET_FPEXC
  37 .\" 2008-04-29 Serge Hallyn, Document PR_CAPBSET_READ and PR_CAPBSET_DROP
  38 .\" 2008-06-13 Erik Bosman, <ejbosman@cs.vu.nl>
  39 .\"     Document PR_GET_TSC and PR_SET_TSC.
  40 .\" 2008-06-15 mtk, Document PR_SET_SECCOMP, PR_GET_SECCOMP
  41 .\" 2009-10-03 Andi Kleen, document PR_MCE_KILL
  42 .\" 2012-04 Cyrill Gorcunov, Document PR_SET_MM
  43 .\" 2012-04-25 Michael Kerrisk, Document PR_TASK_PERF_EVENTS_DISABLE and
  44 .\"                             PR_TASK_PERF_EVENTS_ENABLE
  45 .\" 2012-09-20 Kees Cook, update PR_SET_SECCOMP for mode 2
  46 .\" 2012-09-20 Kees Cook, document PR_SET_NO_NEW_PRIVS, PR_GET_NO_NEW_PRIVS
  47 .\" 2012-10-25 Michael Kerrisk, Document PR_SET_TIMERSLACK and
  48 .\"                             PR_GET_TIMERSLACK
  49 .\" 2013-01-10 Kees Cook, document PR_SET_PTRACER
  50 .\" 2012-02-04 Michael Kerrisk, document PR_{SET,GET}_CHILD_SUBREAPER
  51 .\" 2014-11-10 Dave Hansen, document PR_MPX_{EN,DIS}ABLE_MANAGEMENT
  52 .\"
  53 .\"
  54 .TH PRCTL 2 2016-07-17 "Linux" "Linux Programmer's Manual"
  55 .SH NAME
  56 prctl \- operations on a process
  57 .SH SYNOPSIS
  58 .nf
  59 .B #include <sys/prctl.h>
  60 .sp
  61 .BI "int prctl(int " option ", unsigned long " arg2 ", unsigned long " arg3 ,
  62 .BI "          unsigned long " arg4 ", unsigned long " arg5 );
  63 .fi
  64 .SH DESCRIPTION
  65 .BR prctl ()
  66 is called with a first argument describing what to do
  67 (with values defined in \fI<linux/prctl.h>\fP), and further
  68 arguments with a significance depending on the first one.
  69 The first argument can be:
  70 .\"
  71 .TP
  72 .BR PR_CAP_AMBIENT " (since Linux 4.3)"
  73 .\" commit 58319057b7847667f0c9585b9de0e8932b0fdb08
  74 Reads or changes the ambient capability set, according to the value of
  75 .IR arg2 ,
  76 which must be one of the following:
  77 .RS
  78 .\"
  79 .TP
  80 .B PR_CAP_AMBIENT_RAISE
  81 The capability specified in
  82 .I arg3
  83 is added to the ambient set.
  84 The specified capability must already be present in
  85 both the permitted and the inheritable sets of the process.
  86 This operation is not permitted if the
  87 .B SECBIT_NO_CAP_AMBIENT_RAISE
  88 securebit is set.
  89 .TP
  90 .B PR_CAP_AMBIENT_LOWER
  91 The capability specified in
  92 .I arg3
  93 is removed from the ambient set.
  94 .TP
  95 .B PR_CAP_AMBIENT_IS_SET
  96 The
  97 .BR prctl ()
  98 call returns 1 if the capability in
  99 .I arg3
 100 is in the ambient set and 0 if it is not.
 101 .TP
 102 .BR PR_CAP_AMBIENT_CLEAR_ALL
 103 All capabilities will be removed from the ambient set.
 104 This operation requires setting
 105 .I arg3
 106 to zero.
 107 .RE
 108 .IP
 109 In all of the above operations,
 110 .I arg4
 111 and
 112 .I arg5
 113 must be specified as 0.
 114 .TP
 115 .BR PR_CAPBSET_READ " (since Linux 2.6.25)"
 116 Return (as the function result) 1 if the capability specified in
 117 .I arg2
 118 is in the calling thread's capability bounding set,
 119 or 0 if it is not.
 120 (The capability constants are defined in
 121 .IR <linux/capability.h> .)
 122 The capability bounding set dictates
 123 whether the process can receive the capability through a
 124 file's permitted capability set on a subsequent call to
 125 .BR execve (2).
 126
 127 If the capability specified in
 128 .I arg2
 129 is not valid, then the call fails with the error
 130 .BR EINVAL .
 131 .TP
 132 .BR PR_CAPBSET_DROP " (since Linux 2.6.25)"
 133 If the calling thread has the
 134 .B CAP_SETPCAP
 135 capability within its user namespace, then drop the capability specified by
 136 .I arg2
 137 from the calling thread's capability bounding set.
 138 Any children of the calling thread will inherit the newly
 139 reduced bounding set.
 140
 141 The call fails with the error:
 142 .B EPERM
 143 if the calling thread does not have the
 144 .BR CAP_SETPCAP ;
 145 .BR EINVAL
 146 if
 147 .I arg2
 148 does not represent a valid capability; or
 149 .BR EINVAL
 150 if file capabilities are not enabled in the kernel,
 151 in which case bounding sets are not supported.
 152 .TP
 153 .BR PR_SET_CHILD_SUBREAPER " (since Linux 3.4)"
 154 .\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b
 155 If
 156 .I arg2
 157 is nonzero,
 158 set the "child subreaper" attribute of the calling process;
 159 if
 160 .I arg2
 161 is zero, unset the attribute.
 162
 163 When a process is marked as a child subreaper,
 164 all of the children that it creates, and their descendants,
 165 will be marked as having a subreaper.
 166 In effect, a subreaper fulfills the role of
 167 .BR init (1)
 168 for its descendant processes.
 169 Upon termination of a process
 170 that is orphaned (i.e., its immediate parent has already terminated)
 171 and marked as having a subreaper,
 172 the nearest still living ancestor subreaper
 173 will receive a
 174 .BR SIGCHLD
 175 signal and will be able to
 176 .BR wait (2)
 177 on the process to discover its termination status.
 178 .TP
 179 .BR PR_GET_CHILD_SUBREAPER " (since Linux 3.4)"
 180 Return the "child subreaper" setting of the caller,
 181 in the location pointed to by
 182 .IR "(int\ *) arg2" .
 183 .TP
 184 .BR PR_SET_DUMPABLE " (since Linux 2.3.20)"
 185 Set the state of the "dumpable" flag,
 186 which determines whether core dumps are produced for the calling process
 187 upon delivery of a signal whose default behavior is to produce a core dump.
 188
 189 In kernels up to and including 2.6.12,
 190 .I arg2
 191 must be either 0
 192 .RB ( SUID_DUMP_DISABLE ,
 193 process is not dumpable) or 1
 194 .RB ( SUID_DUMP_USER ,
 195 process is dumpable).
 196 Between kernels 2.6.13 and 2.6.17,
 197 .\" commit abf75a5033d4da7b8a7e92321d74021d1fcfb502
 198 the value 2 was also permitted,
 199 which caused any binary which normally would not be dumped
 200 to be dumped readable by root only;
 201 for security reasons, this feature has been removed.
 202 .\" See http://marc.theaimsgroup.com/?l=linux-kernel&m=115270289030630&w=2
 203 .\" Subject:    Fix prctl privilege escalation (CVE-2006-2451)
 204 .\" From:       Marcel Holtmann <marcel () holtmann ! org>
 205 .\" Date:       2006-07-12 11:12:00
 206 (See also the description of
 207 .I /proc/sys/fs/\:suid_dumpable
 208 in
 209 .BR proc (5).)
 210
 211 Normally, this flag is set to 1.
 212 However, it is reset to the current value contained in the file
 213 .IR /proc/sys/fs/\:suid_dumpable
 214 (which by default has the value 0),
 215 in the following circumstances:
 216 .\" See kernel/cred.c::commit_creds() (Linux 3.18 sources)
 217 .RS
 218 .IP * 3
 219 The process's effective user or group ID is changed.
 220 .IP *
 221 The process's filesystem user or group ID is changed (see
 222 .BR credentials (7)).
 223 .IP *
 224 The process executes
 225 .RB ( execve (2))
 226 a set-user-ID or set-group-ID program,
 227 or a program that has capabilities (see
 228 .BR capabilities (7)).
 229 .\" Also certain namespace operations;
 230 .RE
 231 .IP
 232 Processes that are not dumpable can not be attached via
 233 .BR ptrace (2)
 234 .BR PTRACE_ATTACH ;
 235 see
 236 .BR ptrace (2)
 237 for further details.
 238
 239 If a process is not dumpable,
 240 the ownership of files in the process's
 241 .IR /proc/[pid]
 242 directory is affected as described in
 243 .BR proc (5).
 244 .TP
 245 .BR PR_GET_DUMPABLE " (since Linux 2.3.20)"
 246 Return (as the function result) the current state of the calling
 247 process's dumpable flag.
 248 .\" Since Linux 2.6.13, the dumpable flag can have the value 2,
 249 .\" but in 2.6.13 PR_GET_DUMPABLE simply returns 1 if the dumpable
 250 .\" flags has a nonzero value.  This was fixed in 2.6.14.
 251 .TP
 252 .BR PR_SET_ENDIAN " (since Linux 2.6.18, PowerPC only)"
 253 Set the endian-ness of the calling process to the value given
 254 in \fIarg2\fP, which should be one of the following:
 255 .\" Respectively 0, 1, 2
 256 .BR PR_ENDIAN_BIG ,
 257 .BR PR_ENDIAN_LITTLE ,
 258 or
 259 .B PR_ENDIAN_PPC_LITTLE
 260 (PowerPC pseudo little endian).
 261 .TP
 262 .BR PR_GET_ENDIAN " (since Linux 2.6.18, PowerPC only)"
 263 Return the endian-ness of the calling process,
 264 in the location pointed to by
 265 .IR "(int\ *) arg2" .
 266 .TP
 267 .BR PR_SET_FP_MODE " (since Linux 4.0, only on MIPS)"
 268 .\" commit 9791554b45a2acc28247f66a5fd5bbc212a6b8c8
 269 On the MIPS architecture,
 270 user-space code can be built using an ABI which permits linking
 271 with code that has more restrictive floating-point (FP) requirements.
 272 For example, user-space code may be built to target the O32 FPXX ABI
 273 and linked with code built for either one of the more restrictive
 274 FP32 or FP64 ABIs.
 275 When more restrictive code is linked in,
 276 the overall requirement for the process is to use the more
 277 restrictive floating-point mode.
 278
 279 Because the kernel has no means of knowing in advance
 280 which mode the process should be executed in,
 281 and because these restrictions can
 282 change over the lifetime of the process, the
 283 .B PR_SET_FP_MODE
 284 operation is provided to allow control of the floating-point mode
 285 from user space.
 286
 287 .\" https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking
 288 The
 289 .I (unsigned int) arg2
 290 argument is a bit mask describing the floating-point mode used:
 291 .RS
 292 .TP
 293 .BR PR_FP_MODE_FR
 294 When this bit is
 295 .I unset
 296 (so called
 297 .BR FR=0 " or " FR0
 298 mode), the 32 floating-point registers are 32 bits wide,
 299 and 64-bit registers are represented as a pair of registers
 300 (even- and odd- numbered,
 301 with the even-numbered register containing the lower 32 bits,
 302 and the odd-numbered register containing the higher 32 bits).
 303
 304 When this bit is
 305 .I set
 306 (on supported hardware),
 307 the 32 floating-point registers are 64 bits wide (so called
 308 .BR FR=1 " or " FR1
 309 mode).
 310 Note that modern MIPS implementations (MIPS R6 and newer) support
 311 .B FR=1
 312 mode only.
 313
 314
 315 Applications that use the O32 FP32 ABI can operate only when this bit is
 316 .I unset
 317 .RB ( FR=0 ;
 318 or they can be used with FRE enabled, see below).
 319 Applications that use the O32 FP64 ABI
 320 (and the O32 FP64A ABI, which exists to
 321 provide the ability to operate with existing FP32 code; see below)
 322 can operate only when this bit is
 323 .I set
 324 .RB ( FR=1 ).
 325 Applications that use the O32 FPXX ABI can operate with either
 326 .BR FR=0
 327 or
 328 .BR FR=1 .
 329 .TP
 330 .BR PR_FP_MODE_FRE
 331 Enable emulation of 32-bit floating-point mode.
 332 When this mode is enabled,
 333 it emulates 32-bit floating-point operations
 334 by raising a reserved-instruction exception
 335 on every instruction that uses 32-bit formats and
 336 the kernel then handles the instruction in software.
 337 (The problem lies in the discrepancy of handling odd-numbered registers
 338 which are the high 32 bits of 64-bit registers with even numbers in
 339 .B FR=0
 340 mode and the lower 32-bit parts of odd-numbered 64-bit registers in
 341 .B FR=1
 342 mode.)
 343 Enabling this bit is necessary when code with the O32 FP32 ABI should operate
 344 with code with compatible the O32 FPXX or O32 FP64A ABIs (which require
 345 .B FR=1
 346 FPU mode) or when it is executed on newer hardware (MIPS R6 onwards)
 347 which lacks
 348 .B FR=0
 349 mode support when a binary with the FP32 ABI is used.
 350 .IP
 351 Note that this mode makes sense only when the FPU is in 64-bit mode
 352 .RB ( FR=1 ).
 353 .IP
 354 Note that the use of emulation inherently has a significant performance hit
 355 and should be avoided if possible.
 356 .RE
 357 .IP
 358 In the N32/N64 ABI, 64-bit floating-point mode is always used,
 359 so FPU emulation is not required and the FPU always operates in
 360 .B FR=1
 361 mode.
 362 .IP
 363 This option is mainly intended for use by the dynamic linker
 364 .RB ( ld.so (8)).
 365 .IP
 366 The arguments
 367 .IR arg3 ,
 368 .IR arg4 ,
 369 and
 370 .IR arg5
 371 are ignored.
 372 .TP
 373 .BR PR_GET_FP_MODE " (since Linux 4.0, only on MIPS)"
 374 Get the current floating-point mode (see the description of
 375 .B PR_SET_FP_MODE
 376 for details).
 377
 378 On success,
 379 the call returns a bit mask which represents the current floating-point mode.
 380
 381 The arguments
 382 .IR arg2 ,
 383 .IR arg3 ,
 384 .IR arg4 ,
 385 and
 386 .IR arg5
 387 are ignored.
 388 .TP
 389 .BR PR_SET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"
 390 Set floating-point emulation control bits to \fIarg2\fP.
 391 Pass
 392 .B PR_FPEMU_NOPRINT
 393 to silently emulate floating-point operation accesses, or
 394 .B PR_FPEMU_SIGFPE
 395 to not emulate floating-point operations and send
 396 .B SIGFPE
 397 instead.
 398 .TP
 399 .BR PR_GET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"
 400 Return floating-point emulation control bits,
 401 in the location pointed to by
 402 .IR "(int\ *) arg2" .
 403 .TP
 404 .BR PR_SET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"
 405 Set floating-point exception mode to \fIarg2\fP.
 406 Pass \fBPR_FP_EXC_SW_ENABLE\fP to use FPEXC for FP exception enables,
 407 \fBPR_FP_EXC_DIV\fP for floating-point divide by zero,
 408 \fBPR_FP_EXC_OVF\fP for floating-point overflow,
 409 \fBPR_FP_EXC_UND\fP for floating-point underflow,
 410 \fBPR_FP_EXC_RES\fP for floating-point inexact result,
 411 \fBPR_FP_EXC_INV\fP for floating-point invalid operation,
 412 \fBPR_FP_EXC_DISABLED\fP for FP exceptions disabled,
 413 \fBPR_FP_EXC_NONRECOV\fP for async nonrecoverable exception mode,
 414 \fBPR_FP_EXC_ASYNC\fP for async recoverable exception mode,
 415 \fBPR_FP_EXC_PRECISE\fP for precise exception mode.
 416 .TP
 417 .BR PR_GET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"
 418 Return floating-point exception mode,
 419 in the location pointed to by
 420 .IR "(int\ *) arg2" .
 421 .TP
 422 .BR PR_SET_KEEPCAPS " (since Linux 2.2.18)"
 423 Set the state of the thread's "keep capabilities" flag,
 424 which determines whether the thread's permitted
 425 capability set is cleared when a change is made to the thread's user IDs
 426 such that the thread's real UID, effective UID, and saved set-user-ID
 427 all become nonzero when at least one of them previously had the value 0.
 428 By default, the permitted capability set is cleared when such a change is made;
 429 setting the "keep capabilities" flag prevents it from being cleared.
 430 .I arg2
 431 must be either 0 (permitted capabilities are cleared)
 432 or 1 (permitted capabilities are kept).
 433 (A thread's
 434 .I effective
 435 capability set is always cleared when such a credential change is made,
 436 regardless of the setting of the "keep capabilities" flag.)
 437 The "keep capabilities" value will be reset to 0 on subsequent calls to
 438 .BR execve (2).
 439 .TP
 440 .BR PR_GET_KEEPCAPS " (since Linux 2.2.18)"
 441 Return (as the function result) the current state of the calling thread's
 442 "keep capabilities" flag.
 443 .TP
 444 .BR PR_MCE_KILL " (since Linux 2.6.32)"
 445 Set the machine check memory corruption kill policy for the current thread.
 446 If
 447 .I arg2
 448 is
 449 .BR PR_MCE_KILL_CLEAR ,
 450 clear the thread memory corruption kill policy and use the system-wide default.
 451 (The system-wide default is defined by
 452 .IR /proc/sys/vm/memory_failure_early_kill ;
 453 see
 454 .BR proc (5).)
 455 If
 456 .I arg2
 457 is
 458 .BR PR_MCE_KILL_SET ,
 459 use a thread-specific memory corruption kill policy.
 460 In this case,
 461 .I arg3
 462 defines whether the policy is
 463 .I early kill
 464 .RB ( PR_MCE_KILL_EARLY ),
 465 .I late kill
 466 .RB ( PR_MCE_KILL_LATE ),
 467 or the system-wide default
 468 .RB ( PR_MCE_KILL_DEFAULT ).
 469 Early kill means that the thread receives a
 470 .B SIGBUS
 471 signal as soon as hardware memory corruption is detected inside
 472 its address space.
 473 In late kill mode, the process is killed only when it accesses a corrupted page.
 474 See
 475 .BR sigaction (2)
 476 for more information on the
 477 .BR SIGBUS
 478 signal.
 479 The policy is inherited by children.
 480 The remaining unused
 481 .BR prctl ()
 482 arguments must be zero for future compatibility.
 483 .TP
 484 .BR PR_MCE_KILL_GET " (since Linux 2.6.32)"
 485 Return the current per-process machine check kill policy.
 486 All unused
 487 .BR prctl ()
 488 arguments must be zero.
 489 .TP
 490 .BR PR_SET_MM " (since Linux 3.3)"
 491 .\" commit 028ee4be34a09a6d48bdf30ab991ae933a7bc036
 492 Modify certain kernel memory map descriptor fields
 493 of the calling process.
 494 Usually these fields are set by the kernel and dynamic loader (see
 495 .BR ld.so (8)
 496 for more information) and a regular application should not use this feature.
 497 However, there are cases, such as self-modifying programs,
 498 where a program might find it useful to change its own memory map.
 499 This feature is available only if the kernel is built with the
 500 .BR CONFIG_CHECKPOINT_RESTORE
 501 option enabled.
 502 The calling process must have the
 503 .BR CAP_SYS_RESOURCE
 504 capability.
 505 The value in
 506 .I arg2
 507 is one of the options below, while
 508 .I arg3
 509 provides a new value for the option.
 510 .RS
 511 .TP
 512 .BR PR_SET_MM_START_CODE
 513 Set the address above which the program text can run.
 514 The corresponding memory area must be readable and executable,
 515 but not writable or sharable (see
 516 .BR mprotect (2)
 517 and
 518 .BR mmap (2)
 519 for more information).
 520 .TP
 521 .BR PR_SET_MM_END_CODE
 522 Set the address below which the program text can run.
 523 The corresponding memory area must be readable and executable,
 524 but not writable or sharable.
 525 .TP
 526 .BR PR_SET_MM_START_DATA
 527 Set the address above which initialized and
 528 uninitialized (bss) data are placed.
 529 The corresponding memory area must be readable and writable,
 530 but not executable or sharable.
 531 .TP
 532 .B PR_SET_MM_END_DATA
 533 Set the address below which initialized and
 534 uninitialized (bss) data are placed.
 535 The corresponding memory area must be readable and writable,
 536 but not executable or sharable.
 537 .TP
 538 .BR PR_SET_MM_START_STACK
 539 Set the start address of the stack.
 540 The corresponding memory area must be readable and writable.
 541 .TP
 542 .BR PR_SET_MM_START_BRK
 543 Set the address above which the program heap can be expanded with
 544 .BR brk (2)
 545 call.
 546 The address must be greater than the ending address of
 547 the current program data segment.
 548 In addition, the combined size of the resulting heap and
 549 the size of the data segment can't exceed the
 550 .BR RLIMIT_DATA
 551 resource limit (see
 552 .BR setrlimit (2)).
 553 .TP
 554 .BR PR_SET_MM_BRK
 555 Set the current
 556 .BR brk (2)
 557 value.
 558 The requirements for the address are the same as for the
 559 .BR PR_SET_MM_START_BRK
 560 option.
 561 .P
 562 The following options are available since Linux 3.5.
 563 .\" commit fe8c7f5cbf91124987106faa3bdf0c8b955c4cf7
 564 .TP
 565 .BR PR_SET_MM_ARG_START
 566 Set the address above which the program command line is placed.
 567 .TP
 568 .BR PR_SET_MM_ARG_END
 569 Set the address below which the program command line is placed.
 570 .TP
 571 .BR PR_SET_MM_ENV_START
 572 Set the address above which the program environment is placed.
 573 .TP
 574 .BR PR_SET_MM_ENV_END
 575 Set the address below which the program environment is placed.
 576 .IP
 577 The address passed with
 578 .BR PR_SET_MM_ARG_START ,
 579 .BR PR_SET_MM_ARG_END ,
 580 .BR PR_SET_MM_ENV_START ,
 581 and
 582 .BR PR_SET_MM_ENV_END
 583 should belong to a process stack area.
 584 Thus, the corresponding memory area must be readable, writable, and
 585 (depending on the kernel configuration) have the
 586 .BR MAP_GROWSDOWN
 587 attribute set (see
 588 .BR mmap (2)).
 589 .TP
 590 .BR PR_SET_MM_AUXV
 591 Set a new auxiliary vector.
 592 The
 593 .I arg3
 594 argument should provide the address of the vector.
 595 The
 596 .I arg4
 597 is the size of the vector.
 598 .TP
 599 .BR PR_SET_MM_EXE_FILE
 600 .\" commit b32dfe377102ce668775f8b6b1461f7ad428f8b6
 601 Supersede the
 602 .IR /proc/pid/exe
 603 symbolic link with a new one pointing to a new executable file
 604 identified by the file descriptor provided in
 605 .I arg3
 606 argument.
 607 The file descriptor should be obtained with a regular
 608 .BR open (2)
 609 call.
 610 .IP
 611 To change the symbolic link, one needs to unmap all existing
 612 executable memory areas, including those created by the kernel itself
 613 (for example the kernel usually creates at least one executable
 614 memory area for the ELF
 615 .IR \.text
 616 section).
 617 .IP
 618 The second limitation is that such transitions can be done only once
 619 in a process life time.
 620 Any further attempts will be rejected.
 621 This should help system administrators monitor unusual
 622 symbolic-link transitions over all processes running on a system.
 623 .RE
 624 .TP
 625 .BR PR_MPX_ENABLE_MANAGEMENT ", " PR_MPX_DISABLE_MANAGEMENT " (since Linux 3.19) "
 626 .\" commit fe3d197f84319d3bce379a9c0dc17b1f48ad358c
 627 .\" See also http://lwn.net/Articles/582712/
 628 .\" See also https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler
 629 Enable or disable kernel management of Memory Protection eXtensions (MPX)
 630 bounds tables.
 631 The
 632 .IR arg2 ,
 633 .IR arg3 ,
 634 .IR arg4 ,
 635 and
 636 .IR arg5
 637 .\" commit e9d1b4f3c60997fe197bf0243cb4a41a44387a88
 638 arguments must be zero.
 639
 640 MPX is a hardware-assisted mechanism for performing bounds checking on
 641 pointers.
 642 It consists of a set of registers storing bounds information
 643 and a set of special instruction prefixes that tell the CPU on which
 644 instructions it should do bounds enforcement.
 645 There is a limited number of these registers and
 646 when there are more pointers than registers,
 647 their contents must be "spilled" into a set of tables.
 648 These tables are called "bounds tables" and the MPX
 649 .BR prctl ()
 650 operations control
 651 whether the kernel manages their allocation and freeing.
 652
 653 When management is enabled, the kernel will take over allocation
 654 and freeing of the bounds tables.
 655 It does this by trapping the #BR exceptions that result
 656 at first use of missing bounds tables and
 657 instead of delivering the exception to user space,
 658 it allocates the table and populates the bounds directory
 659 with the location of the new table.
 660 For freeing, the kernel checks to see if bounds tables are
 661 present for memory which is not allocated, and frees them if so.
 662
 663 Before enabling MPX management using
 664 .BR PR_MPX_ENABLE_MANAGEMENT ,
 665 the application must first have allocated a user-space buffer for
 666 the bounds directory and placed the location of that directory in the
 667 .I bndcfgu
 668 register.
 669
 670 These calls will fail if the CPU or kernel does not support MPX.
 671 Kernel support for MPX is enabled via the
 672 .BR CONFIG_X86_INTEL_MPX
 673 configuration option.
 674 You can check whether the CPU supports MPX by looking for the 'mpx'
 675 CPUID bit, like with the following command:
 676
 677         cat /proc/cpuinfo | grep ' mpx '
 678
 679 A thread may not switch in or out of long (64-bit) mode while MPX is
 680 enabled.
 681
 682 All threads in a process are affected by these calls.
 683
 684 The child of a
 685 .BR fork (2)
 686 inherits the state of MPX management.
 687 During
 688 .BR execve (2),
 689 MPX management is reset to a state as if
 690 .BR PR_MPX_DISABLE_MANAGEMENT
 691 had been called.
 692
 693 For further information on Intel MPX, see the kernel source file
 694 .IR Documentation/x86/intel_mpx.txt .
 695 .TP
 696 .BR PR_SET_NAME " (since Linux 2.6.9)"
 697 Set the name of the calling thread,
 698 using the value in the location pointed to by
 699 .IR "(char\ *) arg2" .
 700 The name can be up to 16 bytes long,
 701 .\" TASK_COMM_LEN in include/linux/sched.h
 702 including the terminating null byte.
 703 (If the length of the string, including the terminating null byte,
 704 exceeds 16 bytes, the string is silently truncated.)
 705 This is the same attribute that can be set via
 706 .BR pthread_setname_np (3)
 707 and retrieved using
 708 .BR pthread_getname_np (3).
 709 The attribute is likewise accessible via
 710 .IR /proc/self/task/[tid]/comm ,
 711 where
 712 .I tid
 713 is the name of the calling thread.
 714 .TP
 715 .BR PR_GET_NAME " (since Linux 2.6.11)"
 716 Return the name of the calling thread,
 717 in the buffer pointed to by
 718 .IR "(char\ *) arg2" .
 719 The buffer should allow space for up to 16 bytes;
 720 the returned string will be null-terminated.
 721 .TP
 722 .BR PR_SET_NO_NEW_PRIVS " (since Linux 3.5)"
 723 Set the calling process's
 724 .I no_new_privs
 725 bit to the value in
 726 .IR arg2 .
 727 With
 728 .I no_new_privs
 729 set to 1,
 730 .BR execve (2)
 731 promises not to grant privileges to do anything
 732 that could not have been done without the
 733 .BR execve (2)
 734 call (for example,
 735 rendering the set-user-ID and set-group-ID mode bits,
 736 and file capabilities non-functional).
 737 Once set, this bit cannot be unset.
 738 The setting of this bit is inherited by children created by
 739 .BR fork (2)
 740 and
 741 .BR clone (2),
 742 and preserved across
 743 .BR execve (2).
 744
 745 For more information, see the kernel source file
 746 .IR Documentation/prctl/no_new_privs.txt .
 747 .TP
 748 .BR PR_GET_NO_NEW_PRIVS " (since Linux 3.5)"
 749 Return (as the function result) the value of the
 750 .I no_new_privs
 751 bit for the current process.
 752 A value of 0 indicates the regular
 753 .BR execve (2)
 754 behavior.
 755 A value of 1 indicates
 756 .BR execve (2)
 757 will operate in the privilege-restricting mode described above.
 758 .TP
 759 .BR PR_SET_PDEATHSIG " (since Linux 2.1.57)"
 760 Set the parent death signal
 761 of the calling process to \fIarg2\fP (either a signal value
 762 in the range 1..maxsig, or 0 to clear).
 763 This is the signal that the calling process will get when its
 764 parent dies.
 765 This value is cleared for the child of a
 766 .BR fork (2)
 767 and (since Linux 2.4.36 / 2.6.23)
 768 when executing a set-user-ID or set-group-ID binary,
 769 or a binary that has associated capabilities (see
 770 .BR capabilities (7)).
 771 This value is preserved across
 772 .BR execve (2).
 773
 774 .IR Warning :
 775 .\" https://bugzilla.kernel.org/show_bug.cgi?id=43300
 776 the "parent" in this case is considered to be the
 777 .I thread
 778 that created this process.
 779 In other words, the signal will be sent when that thread terminates
 780 (via, for example,
 781 .BR pthread_exit (3)),
 782 rather than after all of the threads in the parent process terminate.
 783 .TP
 784 .BR PR_GET_PDEATHSIG " (since Linux 2.3.15)"
 785 Return the current value of the parent process death signal,
 786 in the location pointed to by
 787 .IR "(int\ *) arg2" .
 788 .TP
 789 .BR PR_SET_PTRACER " (since Linux 3.4)"
 790 .\" commit 2d514487faf188938a4ee4fb3464eeecfbdcf8eb
 791 .\" commit bf06189e4d14641c0148bea16e9dd24943862215
 792 This is meaningful only when the Yama LSM is enabled and in mode 1
 793 ("restricted ptrace", visible via
 794 .IR /proc/sys/kernel/yama/ptrace_scope ).
 795 When a "ptracer process ID" is passed in \fIarg2\fP,
 796 the caller is declaring that the ptracer process can
 797 .BR ptrace (2)
 798 the calling process as if it were a direct process ancestor.
 799 Each
 800 .B PR_SET_PTRACER
 801 operation replaces the previous "ptracer process ID".
 802 Employing
 803 .B PR_SET_PTRACER
 804 with
 805 .I arg2
 806 set to 0 clears the caller's "ptracer process ID".
 807 If
 808 .I arg2
 809 is
 810 .BR PR_SET_PTRACER_ANY ,
 811 the ptrace restrictions introduced by Yama are effectively disabled for the
 812 calling process.
 813
 814 For further information, see the kernel source file
 815 .IR Documentation/security/Yama.txt .
 816 .TP
 817 .BR PR_SET_SECCOMP " (since Linux 2.6.23)"
 818 .\" See http://thread.gmane.org/gmane.linux.kernel/542632
 819 .\" [PATCH 0 of 2] seccomp updates
 820 .\" andrea@cpushare.com
 821 Set the secure computing (seccomp) mode for the calling thread, to limit
 822 the available system calls.
 823 The more recent
 824 .BR seccomp (2)
 825 system call provides a superset of the functionality of
 826 .BR PR_SET_SECCOMP .
 827
 828 The seccomp mode is selected via
 829 .IR arg2 .
 830 (The seccomp constants are defined in
 831 .IR <linux/seccomp.h> .)
 832
 833 With
 834 .IR arg2
 835 set to
 836 .BR SECCOMP_MODE_STRICT ,
 837 the only system calls that the thread is permitted to make are
 838 .BR read (2),
 839 .BR write (2),
 840 .BR _exit (2)
 841 (but not
 842 .BR exit_group (2)),
 843 and
 844 .BR sigreturn (2).
 845 Other system calls result in the delivery of a
 846 .BR SIGKILL
 847 signal.
 848 Strict secure computing mode is useful for number-crunching applications
 849 that may need to execute untrusted byte code,
 850 perhaps obtained by reading from a pipe or socket.
 851 This operation is available only
 852 if the kernel is configured with
 853 .B CONFIG_SECCOMP
 854 enabled.
 855
 856 With
 857 .IR arg2
 858 set to
 859 .BR SECCOMP_MODE_FILTER " (since Linux 3.5),"
 860 the system calls allowed are defined by a pointer
 861 to a Berkeley Packet Filter passed in
 862 .IR arg3 .
 863 This argument is a pointer to
 864 .IR "struct sock_fprog" ;
 865 it can be designed to filter
 866 arbitrary system calls and system call arguments.
 867 This mode is available only if the kernel is configured with
 868 .B CONFIG_SECCOMP_FILTER
 869 enabled.
 870
 871 If
 872 .BR SECCOMP_MODE_FILTER
 873 filters permit
 874 .BR fork (2),
 875 then the seccomp mode is inherited by children created by
 876 .BR fork (2);
 877 if
 878 .BR execve (2)
 879 is permitted, then the seccomp mode is preserved across
 880 .BR execve (2).
 881 If the filters permit
 882 .BR prctl ()
 883 calls, then additional filters can be added;
 884 they are run in order until the first non-allow result is seen.
 885
 886 For further information, see the kernel source file
 887 .IR Documentation/prctl/seccomp_filter.txt .
 888 .TP
 889 .BR PR_GET_SECCOMP " (since Linux 2.6.23)"
 890 Return (as the function result)
 891 the secure computing mode of the calling thread.
 892 If the caller is not in secure computing mode, this operation returns 0;
 893 if the caller is in strict secure computing mode, then the
 894 .BR prctl ()
 895 call will cause a
 896 .B SIGKILL
 897 signal to be sent to the process.
 898 If the caller is in filter mode, and this system call is allowed by the
 899 seccomp filters, it returns 2; otherwise, the process is killed with a
 900 .BR SIGKILL
 901 signal.
 902 This operation is available only
 903 if the kernel is configured with
 904 .B CONFIG_SECCOMP
 905 enabled.
 906
 907 Since Linux 3.8, the
 908 .IR Seccomp
 909 field of the
 910 .IR /proc/[pid]/status
 911 file provides a method of obtaining the same information,
 912 without the risk that the process is killed; see
 913 .BR proc (5).
 914 .TP
 915 .BR PR_SET_SECUREBITS " (since Linux 2.6.26)"
 916 Set the "securebits" flags of the calling thread to the value supplied in
 917 .IR arg2 .
 918 See
 919 .BR capabilities (7).
 920 .TP
 921 .BR PR_GET_SECUREBITS " (since Linux 2.6.26)"
 922 Return (as the function result)
 923 the "securebits" flags of the calling thread.
 924 See
 925 .BR capabilities (7).
 926 .TP
 927 .BR PR_SET_THP_DISABLE " (since Linux 3.15)"
 928 .\" commit a0715cc22601e8830ace98366c0c2bd8da52af52
 929 Set the state of the "THP disable" flag for the calling thread.
 930 If
 931 .I arg2
 932 has a nonzero value, the flag is set, otherwise it is cleared.
 933 Setting this flag provides a method
 934 for disabling transparent huge pages
 935 for jobs where the code cannot be modified, and using a malloc hook with
 936 .BR madvise (2)
 937 is not an option (i.e., statically allocated data).
 938 The setting of the "THP disable" flag is inherited by a child created via
 939 .BR fork (2)
 940 and is preserved across
 941 .BR execve (2).
 942 .\"
 943 .TP
 944 .BR PR_TASK_PERF_EVENTS_DISABLE " (since Linux 2.6.31)"
 945 Disable all performance counters attached to the calling process,
 946 regardless of whether the counters were created by
 947 this process or another process.
 948 Performance counters created by the calling process for other
 949 processes are unaffected.
 950 For more information on performance counters, see the Linux kernel source file
 951 .IR tools/perf/design.txt .
 952 .IP
 953 Originally called
 954 .BR PR_TASK_PERF_COUNTERS_DISABLE ;
 955 .\" commit 1d1c7ddbfab358445a542715551301b7fc363e28
 956 renamed (with same numerical value)
 957 in Linux 2.6.32.
 958 .\"
 959 .TP
 960 .BR PR_TASK_PERF_EVENTS_ENABLE " (since Linux 2.6.31)"
 961 The converse of
 962 .BR PR_TASK_PERF_EVENTS_DISABLE ;
 963 enable performance counters attached to the calling process.
 964 .IP
 965 Originally called
 966 .BR PR_TASK_PERF_COUNTERS_ENABLE ;
 967 .\" commit 1d1c7ddbfab358445a542715551301b7fc363e28
 968 renamed
 969 .\" commit cdd6c482c9ff9c55475ee7392ec8f672eddb7be6
 970 in Linux 2.6.32.
 971 .\"
 972 .TP
 973 .BR PR_GET_THP_DISABLE " (since Linux 3.15)"
 974 Return (via the function result) the current setting of the "THP disable"
 975 flag for the calling thread:
 976 either 1, if the flag is set, or 0, if it is not.
 977 .TP
 978 .BR PR_GET_TID_ADDRESS " (since Linux 3.5)"
 979 .\" commit 300f786b2683f8bb1ec0afb6e1851183a479c86d
 980 Retrieve the
 981 .I clear_child_tid
 982 address set by
 983 .BR set_tid_address (2)
 984 and the
 985 .BR clone (2)
 986 .B CLONE_CHILD_CLEARTID
 987 flag, in the location pointed to by
 988 .IR "(int\ **)\ arg2" .
 989 This feature is available only if the kernel is built with the
 990 .BR CONFIG_CHECKPOINT_RESTORE
 991 option enabled.
 992 Note that since the
 993 .BR prctl ()
 994 system call does not have a compat implementation for
 995 the AMD64 x32 and MIPS n32 ABIs,
 996 and the kernel writes out a pointer using the kernel's pointer size,
 997 this operation expects a user-space buffer of 8 (not 4) bytes on these ABIs.
 998 .TP
 999 .BR PR_SET_TIMERSLACK " (since Linux 2.6.28)"
1000 .\" See https://lwn.net/Articles/369549/
1001 .\" commit 6976675d94042fbd446231d1bd8b7de71a980ada
1002 Each thread has two associated timer slack values:
1003 a "default" value, and a "current" value.
1004 This operation sets the "current" timer slack value for the calling thread.
1005 If the nanosecond value supplied in
1006 .IR arg2
1007 is greater than zero, then the "current" value is set to this value.
1008 If
1009 .I arg2
1010 is less than or equal to zero,
1011 .\" It seems that it's not possible to set the timer slack to zero;
1012 .\" The minimum value is 1? Seems a little strange.
1013 the "current" timer slack is reset to the
1014 thread's "default" timer slack value.
1015
1016 The "current" timer slack is used by the kernel to group timer expirations
1017 for the calling thread that are close to one another;
1018 as a consequence, timer expirations for the thread may be
1019 up to the specified number of nanoseconds late (but will never expire early).
1020 Grouping timer expirations can help reduce system power consumption
1021 by minimizing CPU wake-ups.
1022
1023 The timer expirations affected by timer slack are those set by
1024 .BR select (2),
1025 .BR pselect (2),
1026 .BR poll (2),
1027 .BR ppoll (2),
1028 .BR epoll_wait (2),
1029 .BR epoll_pwait (2),
1030 .BR clock_nanosleep (2),
1031 .BR nanosleep (2),
1032 and
1033 .BR futex (2)
1034 (and thus the library functions implemented via futexes, including
1035 .\" List obtained by grepping for futex usage in glibc source
1036 .BR pthread_cond_timedwait (3),
1037 .BR pthread_mutex_timedlock (3),
1038 .BR pthread_rwlock_timedrdlock (3),
1039 .BR pthread_rwlock_timedwrlock (3),
1040 and
1041 .BR sem_timedwait (3)).
1042
1043 Timer slack is not applied to threads that are scheduled under
1044 a real-time scheduling policy (see
1045 .BR sched_setscheduler (2)).
1046
1047 When a new thread is created,
1048 the two timer slack values are made the same as the "current" value
1049 of the creating thread.
1050 Thereafter, a thread can adjust its "current" timer slack value via
1051 .BR PR_SET_TIMERSLACK .
1052 The "default" value can't be changed.
1053 The timer slack values of
1054 .IR init
1055 (PID 1), the ancestor of all processes,
1056 are 50,000 nanoseconds (50 microseconds).
1057 The timer slack values are preserved across
1058 .BR execve (2).
1059
1060 Since Linux 4.6, the "current" timer slack value of any process
1061 can be examined and changed via the file
1062 .IR /proc/[pid]/timerslack_ns .
1063 See
1064 .BR proc (5).
1065 .TP
1066 .BR PR_GET_TIMERSLACK " (since Linux 2.6.28)"
1067 Return (as the function result)
1068 the "current" timer slack value of the calling thread.
1069 .TP
1070 .BR PR_SET_TIMING " (since Linux 2.6.0-test4)"
1071 Set whether to use (normal, traditional) statistical process timing or
1072 accurate timestamp-based process timing, by passing
1073 .B PR_TIMING_STATISTICAL
1074 .\" 0
1075 or
1076 .B PR_TIMING_TIMESTAMP
1077 .\" 1
1078 to \fIarg2\fP.
1079 .B PR_TIMING_TIMESTAMP
1080 is not currently implemented
1081 (attempting to set this mode will yield the error
1082 .BR EINVAL ).
1083 .\" PR_TIMING_TIMESTAMP doesn't do anything in 2.6.26-rc8,
1084 .\" and looking at the patch history, it appears
1085 .\" that it never did anything.
1086 .TP
1087 .BR PR_GET_TIMING " (since Linux 2.6.0-test4)"
1088 Return (as the function result) which process timing method is currently
1089 in use.
1090 .TP
1091 .BR PR_SET_TSC " (since Linux 2.6.26, x86 only)"
1092 Set the state of the flag determining whether the timestamp counter
1093 can be read by the process.
1094 Pass
1095 .B PR_TSC_ENABLE
1096 to
1097 .I arg2
1098 to allow it to be read, or
1099 .B PR_TSC_SIGSEGV
1100 to generate a
1101 .B SIGSEGV
1102 when the process tries to read the timestamp counter.
1103 .TP
1104 .BR PR_GET_TSC " (since Linux 2.6.26, x86 only)"
1105 Return the state of the flag determining whether the timestamp counter
1106 can be read,
1107 in the location pointed to by
1108 .IR "(int\ *) arg2" .
1109 .TP
1110 .B PR_SET_UNALIGN
1111 (Only on: ia64, since Linux 2.3.48; parisc, since Linux 2.6.15;
1112 PowerPC, since Linux 2.6.18; Alpha, since Linux 2.6.22;
1113 .\" sh: 94ea5e449ae834af058ef005d16a8ad44fcf13d6
1114 .\" tile: 2f9ac29eec71a696cb0dcc5fb82c0f8d4dac28c9
1115 sh, since Linux 2.6.34; tile, since Linux 3.12)
1116 Set unaligned access control bits to \fIarg2\fP.
1117 Pass
1118 \fBPR_UNALIGN_NOPRINT\fP to silently fix up unaligned user accesses,
1119 or \fBPR_UNALIGN_SIGBUS\fP to generate
1120 .B SIGBUS
1121 on unaligned user access.
1122 Alpha also supports an additional flag with the value
1123 of 4 and no corresponding named constant,
1124 which instructs kernel to not fix up
1125 unaligned accesses (it is analogous to providing the
1126 .BR UAC_NOFIX
1127 flag in
1128 .BR SSI_NVPAIRS
1129 operation of the
1130 .BR setsysinfo ()
1131 system call on Tru64).
1132 .TP
1133 .B PR_GET_UNALIGN
1134 (see
1135 .B PR_SET_UNALIGN
1136 for information on versions and architectures)
1137 Return unaligned access control bits, in the location pointed to by
1138 .IR "(unsigned int\ *) arg2" .
1139 .SH RETURN VALUE
1140 On success,
1141 .BR PR_GET_DUMPABLE ,
1142 .BR PR_GET_KEEPCAPS ,
1143 .BR PR_GET_NO_NEW_PRIVS ,
1144 .BR PR_GET_THP_DISABLE ,
1145 .BR PR_CAPBSET_READ ,
1146 .BR PR_GET_TIMING ,
1147 .BR PR_GET_TIMERSLACK ,
1148 .BR PR_GET_SECUREBITS ,
1149 .BR PR_MCE_KILL_GET ,
1150 .BR PR_CAP_AMBIENT + PR_CAP_AMBIENT_IS_SET ,
1151 and (if it returns)
1152 .BR PR_GET_SECCOMP
1153 return the nonnegative values described above.
1154 All other
1155 .I option
1156 values return 0 on success.
1157 On error, \-1 is returned, and
1158 .I errno
1159 is set appropriately.
1160 .SH ERRORS
1161 .TP
1162 .B EACCES
1163 .I option
1164 is
1165 .BR PR_SET_SECCOMP
1166 and
1167 .I arg2
1168 is
1169 .BR SECCOMP_MODE_FILTER ,
1170 but the process does not have the
1171 .BR CAP_SYS_ADMIN
1172 capability or has not set the
1173 .IR no_new_privs
1174 attribute (see the discussion of
1175 .BR PR_SET_NO_NEW_PRIVS
1176 above).
1177 .TP
1178 .B EACCES
1179 .I option
1180 is
1181 .BR PR_SET_MM ,
1182 and
1183 .I arg3
1184 is
1185 .BR PR_SET_MM_EXE_FILE ,
1186 the file is not executable.
1187 .TP
1188 .B EBADF
1189 .I option
1190 is
1191 .BR PR_SET_MM ,
1192 .I arg3
1193 is
1194 .BR PR_SET_MM_EXE_FILE ,
1195 and the file descriptor passed in
1196 .I arg4
1197 is not valid.
1198 .TP
1199 .B EBUSY
1200 .I option
1201 is
1202 .BR PR_SET_MM ,
1203 .I arg3
1204 is
1205 .BR PR_SET_MM_EXE_FILE ,
1206 and this the second attempt to change the
1207 .I /proc/pid/exe
1208 symbolic link, which is prohibited.
1209 .TP
1210 .B EFAULT
1211 .I arg2
1212 is an invalid address.
1213 .TP
1214 .B EFAULT
1215 .I option
1216 is
1217 .BR PR_SET_SECCOMP ,
1218 .I arg2
1219 is
1220 .BR SECCOMP_MODE_FILTER ,
1221 the system was built with
1222 .BR CONFIG_SECCOMP_FILTER ,
1223 and
1224 .I arg3
1225 is an invalid address.
1226 .TP
1227 .B EINVAL
1228 The value of
1229 .I option
1230 is not recognized.
1231 .TP
1232 .B EINVAL
1233 .I option
1234 is
1235 .BR PR_MCE_KILL
1236 or
1237 .BR PR_MCE_KILL_GET
1238 or
1239 .BR PR_SET_MM ,
1240 and unused
1241 .BR prctl ()
1242 arguments were not specified as zero.
1243 .TP
1244 .B EINVAL
1245 .I arg2
1246 is not valid value for this
1247 .IR option .
1248 .TP
1249 .B EINVAL
1250 .I option
1251 is
1252 .BR PR_SET_SECCOMP
1253 or
1254 .BR PR_GET_SECCOMP ,
1255 and the kernel was not configured with
1256 .BR CONFIG_SECCOMP .
1257 .TP
1258 .B EINVAL
1259 .I option
1260 is
1261 .BR PR_SET_SECCOMP ,
1262 .I arg2
1263 is
1264 .BR SECCOMP_MODE_FILTER ,
1265 and the kernel was not configured with
1266 .BR CONFIG_SECCOMP_FILTER .
1267 .TP
1268 .B EINVAL
1269 .I option
1270 is
1271 .BR PR_SET_MM ,
1272 and one of the following is true
1273 .RS
1274 .IP * 3
1275 .I arg4
1276 or
1277 .I arg5
1278 is nonzero;
1279 .IP *
1280 .I arg3
1281 is greater than
1282 .B TASK_SIZE
1283 (the limit on the size of the user address space for this architecture);
1284 .IP *
1285 .I arg2
1286 is
1287 .BR PR_SET_MM_START_CODE ,
1288 .BR PR_SET_MM_END_CODE ,
1289 .BR PR_SET_MM_START_DATA ,
1290 .BR PR_SET_MM_END_DATA ,
1291 or
1292 .BR PR_SET_MM_START_STACK ,
1293 and the permissions of the corresponding memory area are not as required;
1294 .IP *
1295 .I arg2
1296 is
1297 .BR PR_SET_MM_START_BRK
1298 or
1299 .BR PR_SET_MM_BRK ,
1300 and
1301 .I arg3
1302 is less than or equal to the end of the data segment
1303 or specifies a value that would cause the
1304 .B RLIMIT_DATA
1305 resource limit to be exceeded.
1306 .RE
1307 .TP
1308 .B EINVAL
1309 .I option
1310 is
1311 .BR PR_SET_PTRACER
1312 and
1313 .I arg2
1314 is not 0,
1315 .BR PR_SET_PTRACER_ANY ,
1316 or the PID of an existing process.
1317 .TP
1318 .B EINVAL
1319 .I option
1320 is
1321 .B PR_SET_PDEATHSIG
1322 and
1323 .I arg2
1324 is not a valid signal number.
1325 .TP
1326 .B EINVAL
1327 .I option
1328 is
1329 .BR PR_SET_DUMPABLE
1330 and
1331 .I arg2
1332 is neither
1333 .B SUID_DUMP_DISABLE
1334 nor
1335 .BR SUID_DUMP_USER .
1336 .TP
1337 .B EINVAL
1338 .I option
1339 is
1340 .BR PR_SET_TIMING
1341 and
1342 .I arg2
1343 is not
1344 .BR PR_TIMING_STATISTICAL .
1345 .TP
1346 .B EINVAL
1347 .I option
1348 is
1349 .BR PR_SET_NO_NEW_PRIVS
1350 and
1351 .I arg2
1352 is not equal to 1
1353 or
1354 .IR arg3 ,
1355 .IR arg4 ,
1356 or
1357 .IR arg5
1358 is nonzero.
1359 .TP
1360 .B EINVAL
1361 .I option
1362 is
1363 .BR PR_GET_NO_NEW_PRIVS
1364 and
1365 .IR arg2 ,
1366 .IR arg3 ,
1367 .IR arg4 ,
1368 or
1369 .IR arg5
1370 is nonzero.
1371 .TP
1372 .B EINVAL
1373 .I option
1374 is
1375 .BR PR_SET_THP_DISABLE
1376 and
1377 .IR arg3 ,
1378 .IR arg4 ,
1379 or
1380 .IR arg5
1381 is nonzero.
1382 .TP
1383 .B EINVAL
1384 .I option
1385 is
1386 .BR PR_GET_THP_DISABLE
1387 and
1388 .IR arg2 ,
1389 .IR arg3 ,
1390 .IR arg4 ,
1391 or
1392 .IR arg5
1393 is nonzero.
1394 .TP
1395 .B EINVAL
1396 .I option
1397 is
1398 .B PR_CAP_AMBIENT
1399 and an unused argument
1400 .RI ( arg4 ,
1401 .IR arg5 ,
1402 or,
1403 in the case of
1404 .BR PR_CAP_AMBIENT_CLEAR_ALL ,
1405 .IR arg3 )
1406 is nonzero; or
1407 .IR arg2
1408 has an invalid value;
1409 or
1410 .IR arg2
1411 is
1412 .BR PR_CAP_AMBIENT_LOWER ,
1413 .BR PR_CAP_AMBIENT_RAISE ,
1414 or
1415 .BR PR_CAP_AMBIENT_IS_SET
1416 and
1417 .IR arg3
1418 does not specify a valid capability.
1419 .TP
1420 .B ENXIO
1421 .I option
1422 was
1423 .BR PR_MPX_ENABLE_MANAGEMENT
1424 or
1425 .BR PR_MPX_DISABLE_MANAGEMENT
1426 and the kernel or the CPU does not support MPX management.
1427 Check that the kernel and processor have MPX support.
1428 .TP
1429 .B EOPNOTSUPP
1430 .I option
1431 is
1432 .B PR_SET_FP_MODE
1433 and
1434 .I arg2
1435 has an invalid or unsupported value.
1436 .TP
1437 .B EPERM
1438 .I option
1439 is
1440 .BR PR_SET_SECUREBITS ,
1441 and the caller does not have the
1442 .B CAP_SETPCAP
1443 capability,
1444 or tried to unset a "locked" flag,
1445 or tried to set a flag whose corresponding locked flag was set
1446 (see
1447 .BR capabilities (7)).
1448 .TP
1449 .B EPERM
1450 .I option
1451 is
1452 .BR PR_SET_KEEPCAPS ,
1453 and the caller's
1454 .B SECURE_KEEP_CAPS_LOCKED
1455 flag is set
1456 (see
1457 .BR capabilities (7)).
1458 .TP
1459 .B EPERM
1460 .I option
1461 is
1462 .BR PR_CAPBSET_DROP ,
1463 and the caller does not have the
1464 .B CAP_SETPCAP
1465 capability.
1466 .TP
1467 .B EPERM
1468 .I option
1469 is
1470 .BR PR_SET_MM ,
1471 and the caller does not have the
1472 .B CAP_SYS_RESOURCE
1473 capability.
1474 .TP
1475 .B EPERM
1476 .IR option
1477 is
1478 .BR PR_CAP_AMBIENT
1479 and
1480 .IR arg2
1481 is
1482 .BR PR_CAP_AMBIENT_RAISE ,
1483 but either the capability specified in
1484 .IR arg3
1485 is not present in the process's permitted and inheritable capability sets,
1486 or the
1487 .B PR_CAP_AMBIENT_LOWER
1488 securebit has been set.
1489 .SH VERSIONS
1490 The
1491 .BR prctl ()
1492 system call was introduced in Linux 2.1.57.
1493 .\" The library interface was added in glibc 2.0.6
1494 .SH CONFORMING TO
1495 This call is Linux-specific.
1496 IRIX has a
1497 .BR prctl ()
1498 system call (also introduced in Linux 2.1.44
1499 as irix_prctl on the MIPS architecture),
1500 with prototype
1501 .sp
1502 .BI "ptrdiff_t prctl(int " option ", int " arg2 ", int " arg3 );
1503 .sp
1504 and options to get the maximum number of processes per user,
1505 get the maximum number of processors the calling process can use,
1506 find out whether a specified process is currently blocked,
1507 get or set the maximum stack size, and so on.
1508 .SH SEE ALSO
1509 .BR signal (2),
1510 .BR core (5)